SuhjamUies, Genera, and Subgenera — Recent and Fossil 69 



Digestive System. The stoiiiacli (plate 48, fig. 13j is cylindrical with 

 the crop, gizzard, and jndoris plainly indicated. The intestine, after leaving 

 the in'loris, makes a looj) over the oesophagus which extends backward, 

 around the liver, and then loops forward to the rectum which has its exit 

 on the pseudobranch. All species of typical Gyraulus examined have the 

 same type of stomach and intestine. The buccal sac (of Gyraulus albun 

 plate 70, fig. 13) is pyriform with the radula sac greatly developed and 

 protruding behind (RL). The salivary glands (SG) are elongated, cylin- 

 drical, and almost as long as the buccal sac. The ducts of these glands 

 are long. 



The jaw (plate 50) is horseshoe-shaped and fragmented as in Planorbis 

 and Anisus. Gyraulus hirsutus (fig. 17) has large plates, about forty on 

 the entire jaw. Gyraulus albus has the same number. In Gyraulus dejiectus 

 obliquus (fig. 18) the jaw is arched and consists of over fifty plates which 

 are narrower than those of albus and hirsutv^. In latestomus the jaw is 

 similar to that of obliquus and has over forty plates. 



The radula formula of Gyraulus albus (plate 68, fig. 9) is 18-1-18 with 

 103 to 114 rows of teeth. The center tooth is bicuspid, the cusps long and 

 narrow and reaching only about half waj- to the lower margin of the base 

 of attachment. The laterals (1-9) are tricuspid with long, narrow cusps. 

 The cusps of intermediate teeth ( 10-11 ) are short, placed high up on the re- 

 flection, and the ectocone is split into two sharp cusps. The marginal teeth 

 (12-18) have the reflection high up on the tooth, are wide and low and 

 6-cuspid. The entocone is split into two small cusps, the mesocone is larger, 

 and the ectocone cusps, three in number, are very small and sharp. In sev- 

 eral membranes examined a very small 4th cusp appears on the 6th tooth 

 and continues to the intermediate teeth. The center tooth varies in size in 

 the 43rd to 62nd rows being a trifle wider at the top than in the first forty- 

 two rows. The 86th to 103rd rows have a central tooth a little more than 

 half the width of those in the 43rd to 62nd rows. 



The radula of Gyraulus hirsutus (plate 69, fig. 1) is similar to that of 

 albus. The formula is 19-1-19, with 1-9 lateral teeth, 10-11 intermediate 

 teeth, and 12-19 marginal teeth. There are 130 rows of teeth. The radula of 

 Gyraulus dejiectus obliquus (plate 69, fig. 2) has a formula of 22-1-22, 

 with 1-9 lateral teeth, 10-13 intermediate teeth, and 14-22 marginal teeth. 

 There are 175 to 183 rows. Gyraulus latestomus has the formula 20-1-20, 

 with 1-10 marginal teeth, 11-14 intermediate teeth, and 15-20 marginal 

 teeth. There are 155 rows of teeth. 



Gyraulus convexiusculus has the formula 20-1-20, with 1-9 lateral 

 teeth, 10-13 intermediate teeth, and 14-20 marginal teeth. The specimens 

 examined differ from the figure by Annandale and Prashad (Rec. Ind. 

 AIus., XVni, p. 55, fig. 8, B) where the inner laterals are shown as bi- 

 cuspid, an unusual condition in the genus. Probably the entocones were 

 not observed, for they were present in all of the laterals of the teeth per- 

 sonally examined. The figure of the radula of Gyraulus euphraticu^ (C) 

 by Annandale and Prashad is more correct in the tricuspid character of 

 the lateral teeth. The radulae of all of the typical Gyraidus examined have 

 been similar in character. 



For the above anatomical data the following material has been 

 available: 

 G. olbu.s, 25 specimens from park in Krolikarnia, a suburb of "Warsaw, Poland. 



Collected bv Mr. A. Jankowski. 



